[v3,04/10] kvm: kvm_get_writable_id_regs

Commit Message

Cornelia Huck April 14, 2025, 4:38 p.m. UTC

Add an helper to retrieve the writable id reg bitmask. The
status of the query is stored in the CPU struct so that an
an error, if any, can be reported on vcpu realize().

Signed-off-by: Eric Auger <[e-mail]>
Signed-off-by: Cornelia Huck <[e-mail]>
---
 target/arm/cpu.h     | 26 ++++++++++++++++++++++++++
 target/arm/kvm.c     | 32 ++++++++++++++++++++++++++++++++
 target/arm/kvm_arm.h |  7 +++++++
 3 files changed, 65 insertions(+)

Patch

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index d27134f4a025..bbee7ff2414a 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -856,6 +856,26 @@  typedef struct {
     uint32_t map, init, supported;
 } ARMVQMap;
 
+typedef enum ARMIdRegsState {
+    WRITABLE_ID_REGS_UNKNOWN,
+    WRITABLE_ID_REGS_NOT_DISCOVERABLE,
+    WRITABLE_ID_REGS_FAILED,
+    WRITABLE_ID_REGS_AVAIL,
+} ARMIdRegsState;
+
+/*
+ * The following structures are for the purpose of mapping the output of
+ * KVM_ARM_GET_REG_WRITABLE_MASKS that also may cover id registers we do
+ * not support in QEMU
+ * ID registers in op0==3, op1=={0,1,3}, crn=0, crm=={0-7}, op2=={0-7},
+ * as used by the KVM_ARM_GET_REG_WRITABLE_MASKS ioctl call.
+ */
+#define NR_ID_REGS (3 * 8 * 8)
+
+typedef struct IdRegMap {
+    uint64_t regs[NR_ID_REGS];
+} IdRegMap;
+
 /* REG is ID_XXX */
 #define FIELD_DP64_IDREG(ISAR, REG, FIELD, VALUE)                       \
     ({                                                                  \
@@ -1044,6 +1064,12 @@  struct ArchCPU {
      */
     bool host_cpu_probe_failed;
 
+    /*
+     * state of writable id regs query used to report an error, if any,
+     * on KVM custom vcpu model realize
+     */
+    ARMIdRegsState writable_id_regs;
+
     /* QOM property to indicate we should use the back-compat CNTFRQ default */
     bool backcompat_cntfrq;
 
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 8491f42a18d2..6e3cd06e9bc5 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -50,6 +50,7 @@  const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
 static bool cap_has_mp_state;
 static bool cap_has_inject_serror_esr;
 static bool cap_has_inject_ext_dabt;
+static int cap_writable_id_regs;
 
 /**
  * ARMHostCPUFeatures: information about the host CPU (identified
@@ -488,6 +489,37 @@  void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     env->features = arm_host_cpu_features.features;
 }
 
+int kvm_arm_get_writable_id_regs(ARMCPU *cpu, IdRegMap *idregmap)
+{
+    struct reg_mask_range range = {
+        .range = 0, /* up to now only a single range is supported */
+        .addr = (uint64_t)idregmap,
+    };
+    int ret;
+
+    if (!kvm_enabled()) {
+        cpu->writable_id_regs = WRITABLE_ID_REGS_NOT_DISCOVERABLE;
+        return -ENOSYS;
+    }
+
+    cap_writable_id_regs =
+        kvm_check_extension(kvm_state, KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES);
+
+    if (!cap_writable_id_regs ||
+        !(cap_writable_id_regs & (1 << KVM_ARM_FEATURE_ID_RANGE))) {
+        cpu->writable_id_regs = WRITABLE_ID_REGS_NOT_DISCOVERABLE;
+        return -ENOSYS;
+    }
+
+    ret = kvm_vm_ioctl(kvm_state, KVM_ARM_GET_REG_WRITABLE_MASKS, &range);
+    if (ret) {
+        cpu->writable_id_regs = WRITABLE_ID_REGS_FAILED;
+        return ret;
+     }
+    cpu->writable_id_regs = WRITABLE_ID_REGS_AVAIL;
+    return ret;
+}
+
 static bool kvm_no_adjvtime_get(Object *obj, Error **errp)
 {
     return !ARM_CPU(obj)->kvm_adjvtime;
diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index 05c3de8cd46e..8d1f20ca8d89 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -221,6 +221,8 @@  int kvm_arm_set_irq(int cpu, int irqtype, int irq, int level);
 
 void kvm_arm_enable_mte(Object *cpuobj, Error **errp);
 
+int kvm_arm_get_writable_id_regs(ARMCPU *cpu, IdRegMap *idregmap);
+
 #else
 
 /*
@@ -247,6 +249,11 @@  static inline bool kvm_arm_mte_supported(void)
     return false;
 }
 
+static inline int kvm_arm_get_writable_id_regs(ARMCPU *cpu, IdRegMap *idregmap)
+{
+    return -ENOSYS;
+}
+
 /*
  * These functions should never actually be called without KVM support.
  */